1. Field of the Invention
The present invention relates to a method for manufacturing a unidirectionally-oriented hollow ceramic fiber aggregate using as a mold a fiber aggregate of organic fibers unidirectionally oriented by electrostatic means, and more particularly to a technology for manufacturing a ceramic fiber aggregate by which a ceramic fiber aggregate with a micron-scale hollow structure and with a unidirectional orientation can be formed by dipping the aforementioned fiber aggregate in a ceramics base solution (ceramics material or ceramics material precursor) to form a ceramics fiber precursor with an organic-inorganic structure, and treating the precursor by heat or other means to remove the organic fiber aggregate from the ceramics fiber precursor.
2. Description of the Related Art
In general, porous ceramic bodies show great promise in a variety of fields including adsorption and separation. The IUPAC classification divides porous bodies into microporous bodies with a pore size of less than 2 nm, mesoporous bodies with a pore size of 2-50 nm and macroporous bodies with a pore size over 50 nm. If it were possible to control the pore size of porous bodies freely and precisely, they would open the door to such applications as selective adsorbent and catalyst materials and high separation materials.
Known methods of producing mesoporous and macroporous materials include methods, wherein as the mold a molecular aggregate of surfactants, an aggregate containing both surfactant molecules and specific organic molecules, or a molecular aggregate of different kinds of surfactants is used. Because the maximum pore size obtained with these organic molecules is about 30 nm, they cannot be used as filters for selectively separating bacteria (0.5-5 xcexcmxcfx86), molds (hyphae 5-30 xcexcm, spores 3-10 xcexcm), or viruses (150-180 nm).
There are conventional, commercially available ceramic filters in which the pore size is controlled above submicroscopic level by dispersing and baking of bulk powder, and because the ceramic grains in the filters are randomly arranged in 2 and 3 dimensions, bacteria, dust, and the like becomes trapped in gaps between the grains when the gas or liquid containing them passes through the gaps. Because the gaps are very irregular, however, it is difficult to trap bacteria and the like efficiently in the filter, and clogging of the gaps is occurred also frequently, necessitating treatment such as back washing is requested. More efficient separation might be achieved and clogging of the gaps might be prevented if the gas or liquid were passed through the hollows of a micron-scale hollow structure in which the pores were unidirectionally aligned. Attempts have been made in the past to obtain a porous body by adding combustible organic fibers, but there have been almost no attempts to obtain a porous body by using organic fiber molds with the organic fibers unidirectionally arranged. There have also been efforts to form cavities by using separate phase glass or the eutectic effect, but it is difficult to create through holes.
As described above, a ceramic fiber aggregate with a micron-scale hollow structure can be obtained by using as a mold an organic fiber aggregate of silk, cotton or the like to form a ceramic fiber precursor with an organic-inorganic structure, and removing the organic fiber aggregate from the precursor by treatment with heat or organic solvents, but of the conventional processes using organic fiber molds, almost none include unidirectional control of the organic fibers.
With the foregoing in view, the inventors have succeeded after dedicated research in forming a unidirectionally-oriented organic fiber aggregate by setting 0.1-50 mm sections of organic fiber dispersed in dielectric liquid between positive and negative electrodes with a high voltage charge and electrostatically aligning the individual fibers in the dielectric liquid with one end towards the positive electrode and the other towards the negative electrode, and then have discovered that ceramic fiber can be produced having a micron-scale hollow structure with unidirectionally-oriented pores by using the organic fiber aggregate as a mold to form a ceramic fiber precursor with an inorganic-organic structure, and then treating the precursor with heat, organic solvents or the like to break down and remove the organic fibers, leaving only the inorganic structure, and the present invention has been perfected based on these findings.
A method is provided of manufacturing hollow ceramics fibers using a mold of organic fibers unidirectionally oriented by electrostatic means. The present invention relates to a method of manufacturing hollow ceramics fibers with the pores of the micron-scale hollow structure unidirectionally oriented, the method of manufacturing is characterized in the steps of dispersing organic fibers in a dielectric liquid and applying high voltage to the dielectric liquid containing the dispersed organic fibers to electrostatically align them to produce a fiber accumulation in which the organic fibers are unidirectionally oriented, using said fiber accumulation as a mold and dipping said fiber accumulation in a ceramics base solution, and then removing said mold by treatment with heat or organic solvents.
Namely, an object of the present invention is to provide a means of producing a ceramic fiber aggregate with a micron-scale hollow structure consisting of an inorganic skeleton, by unidirectionally aligning organic fibers by electrostatic means, and then using the resulting aligned organic fiber aggregate as a mold to produce the hollow ceramics fibers.
In order to solve the problems described above, the present invention comprises the following technical means.
(1) A method of manufacturing hollow ceramics fibers with the pores of the micron-scale hollow structure unidirectionally oriented, the method for manufacturing is characterized in the steps of dispersing organic fibers in a dielectric liquid and applying high voltage to the dielectric liquid containing said organic fibers to electrostatically align them and to produce a fiber accumulation of unidirectionally-oriented organic fibers, taking the fiber accumulation as a mold and dipping it in a ceramics base solution, and removing the mold by treatment with heat or organic solvents.
(2) The method for manufacturing hollow ceramics fibers unidirectionally-oriented described above (1), wherein the organic fiber is one selected from the group of raw silk, cotton, hemp, nylon, polyester, acrylic, cellulose and chitin.
(3) The method for manufacturing hollow ceramics fibers unidirectionally-oriented described above (1), wherein the ceramics base solution is composed of an alkoxide or chloride of titanium, aluminum, zirconium, silicon or the like and alcohol, and optional water, hydrochloric acid or the like.
(4) The method for manufacturing hollow ceramics fibers unidirectionally-oriented described above (1), wherein the ceramics base solution is formed from polyethylene glycol, surfactants and organic polymers such as block copolymer in addition to an alkoxide or chloride of titanium, aluminum, zirconium or silicon and alcohol, and optional water, hydrochloric acid or the like.
(5) The method for manufacturing hollow ceramics fibers unidirectionally-oriented described above (1), wherein dipping is performed by the dip coating, dipping or spin coating method.
(6) The method for manufacturing hollow ceramics fibers unidirectionally-oriented described above (1), wherein the mold is removed by treatment with heat or organic solvents.